2000A&A...363..667S

We report on a large X-ray flare from the Lindroos binary system HD 560 during a pointed ROSAT PSPC observation. HD 560 is composed of a B9 and a G5 type star. The late-type companions in bound Lindroos binaries are Post T Tauri star (PTTS) candidates, i.e. pre-main sequence stars on their final approach to the main sequence. Strong (magnetic) activity is, therefore, expected for the G star, in contrast to the late-B type component for which no mechanism of X-ray production is known. The system is unresolved in the ROSAT image. During outburst the count rate has changed by at least a factor of 2, and presumably more (the maximum was not observed). The peak luminosity measured is ∼10³¹erg/s, comparable to the largest values derived for flares on pre-main sequence T Tauri stars. A two-temperature model for thermal emission from a hot, optically thin plasma shows an increase of the higher temperature as a result of coronal heating during the flare. The lower temperatures do not change during outburst.